Composition of baths for electrodeposition of bright zinc from aqueous, acid, electroplating baths

ABSTRACT

It has been found that upon addition to an aqueous, acid, zinc electroplating bath, naphthol polyoxyalkylate and polyethylenimine act synergistically to provide smooth, bright, ductile, electrodeposits of zinc.

United States Patent 1 Rosenberg 1 Mar. 27, 1973 COMPOSITION OF BATHS FOR ELECTRODEPOSITION OF BRIGHT ZINC FROM AQUEOUS, ACID, ELECTROPLATING BATHS Inventor: William E. Rosenberg, Parma, Ohio Assignee: R. 0. Hull & Company, Inc., Cleveland, Ohio Filed: Feb. 25, 1972 Appl. No.2 229,590

U.S. Cl. ..204/55 R, 204/DIG. 2 Int. Cl. ..C23b 5/12, C23b 5/46 Field of Search ....204/55 R, 55 Y, 43, 44, 114

References Cited UNITED STATES PATENTS Harford ..204/55 R X Harford Pye et a1 Rosenberg... Wade ..204/55 R X Primary Examiner-G. L. Kaplan Y Attorney-Blythe D. Watts et al.

ABSTRACT 4 Claims, N0 Drawings COMPOSITION OF BATIIS FOR ELECTRODEPOSITION OF BRIGHT ZINC FROM AQUEOUS, ACII), ELECTROPLATING BATI-IS BACKGROUND OF THE INVENTION This invention pertains to improvements in the electrodeposition of bright zinc from aqueous acid plating baths.

Acid zinc electroplating baths are not new in the plating field and have, in fact, been used with moderate success for quite some time. Prior to this invention, however, certain limitations have in many instances rendered the existing acid zinc plating bath compositions extremely impractical to use and quite often not applicable at all.

One of the most limiting factors in the plating of bright zinc from acid plating baths has been that only a rather low current density could be applied to a given part to produce a lustrous zinc deposit. By raising the current density to increase the speed of plating, the plater would encounter dark, coarse, and even spongy deposits of zinc.

Another problem that has been common has been the lack of ductility in the zinc plate obtained from existing acid zinc bath compositions. Many parts are bent or shaped after plating either through manufacturing processes or through normal use. If the electrodeposit is not reasonably ductile, chipping, flaking and peeling of the plate can occur, thus causing rejection of the part.

Many of the addition agents prior to this invention have been considerably intolerant to operating temperatures higher than 90 F. These additives would either be chemically destroyed at higher temperatures or just lose their ability to produce bright deposits.

The addition agents and bath compositions of this invention have overcome these serious limitations. With the use of this invention, much higher current densities and operating temperatures can be used to obtain lustrous, bright, ductile deposits of zinc from acid zinc plating baths. This is possible because these additives provide bright deposits over a very wide current density range, are chemically stable, and are not adversely affected by normal increases in temperature.

SUMMARY OF THE INVENTION This invention comprises an aqueous, acid electroplating bath, for producing a bright, lustrous electrodeposit of zinc containing zinc ions and chloride ions, and dissolved therein, naphthol polyoxyalkylate having the formula:

where R is hydrogen or methyl, and x is about 8 to 20. and polyethylenimine having the formula:

where R is hydrogen, methyl, ethyl, propyl, hydroxyethyl, Z-hydroxypropyl, 3-hydroxypropyl, 2- aminoethyl, 2-aminopropyl, or 3-aminopropyl, and y is about 10 to 20.

The present invention is also an addition agent for an acid zinc electroplating bath consisting of from about 1:100 to :1 parts by weight of naphthol polyoxyalkylate and polyethylenimine of the above formulas.

DETAILED DESCRIPTION Both the naphthol polyoxyalkylates and the polyethylenimines of this invention are available in commerce and are supplied as viscous oils and aqueous solutions.

For ease of handling the addition agents were made up as aqueous solutions, but any other suitable solvent or emulsion will work as well.

All testing was done in a conventional 267 ml. I-Iull Cell using steel cathode panels and a zinc anode. Two ampere panels were run for 10 minutes at temperatures ranging from 70 to F. with mechanical agitation.

A general purpose bath was made up which contained 30 gms. ZnCl /liter and 200 gms. NH,Cl/liter at a pH of 4.9.

Addition of between 0.1 to 20 gms. of naphthol polyoxyalkylate to the general purpose bath produces only a semi-bright cloudy electrodeposit of zinc from 0 to about 40 amps. per sq. ft. The current density area from 40 amps. per sq. ft. up to 200 amps. per sq. ft. is left as a dark, rough and somewhat spongy electrodeposit.

Similarly, the singular addition of about 0.1 to 20 gms. per liter of polyethylenimine to this bath gives only a semibright, gray electrodeposit from about 50 amps. per sq. ft. up to 200 amps per sq. ft.

The current density area from 0 to about 50 amps per sq. ft. is left as a dark, rough electrodeposit with no trace of brightness.

When the naphthol polyoxyalkylate and the polyethylenimine are added together to this general purpose bath, they act synergistically to provide a bright, lustrous electrodeposit from about 12 amps per sq. ft. to well over 200 amps per sq. ft. In addition to being extremely bright, the deposit is quite ductile. The current densities below 12 amps per sq. ft. can be made bright by the addition of between 0.01 and 10 gms. per liter of a substance selected from the group consisting of anisaldehyde, piperonal, veratraldehyde, benzaldehyde, vanillan, benzylidene acetone, and cinnamic aldehyde.

While the addition agents of this invention are effective in many aqueous, acid zinc plating bath formulations, it is preferred to use any of the basic baths described in the following examples. It will be understood that the following examples are just illustrations and are not meant to limit the use of the invention to these bath compositions only:

EX AM PLE I Bath Composition Concentrations in gms/liter Zinc Chloride 30 Ammonium Chloride 200 pH 5.0 Polyethylenimine 4 (600 molecular weight) b-naphthol polyoxyethylene 4 (12 moles of ethylene oxide) EXAM PLE II Bath Composition Concentration in gms/liter Zinc Sulfate 34 Ammonium Chloride 150 pH 4,8 N-hydroxyethyl polyethylenimine (1,200 molecular weight) b-naphthol polyethylene oxide 10 (I5 moles of ethylene oxide) EXAM PLE III Bath Composition Concentration in gms/liter Zinc chloride 60 Ammonium Chloride 200 pH 5.0 Polyethylenimine 4 (600 molecular weight) b-naphthol polyethylene oxide 4 (8 moles of ethylene oxide) Piperonal (added as methanol solution) EX AM PLE IV Bath Composition Concentration in gms/liter Zinc Chloride 30 Ammonium Chloride 200 pH 6.0 2-hydroxy propyl polyethylenimine (I200 molecular weight) 8 a'naphthol polyethylene oxide 5 moles ethylene oxide) Benzaldehyde (added as methanol ([2 moles ethylene oxide) Having thus described this invention in such full, clear, concise and exact terms as to enable any person skilled in the art to which it pertains to make and use the same, and having set forth the best mode contemplated of carrying out this invention, I state that the subject matter which I regard as being my invention is particularly pointed out and dinstinctly claimed in what is claimed, it being understood that equivalents or modifications of, or substitutions for, parts of the above specifically described embodiment of the invention may be made without departing from the scope of the invention as set forth in what is claimed.

What is claimed is:

1. An aqueous, acid electroplating bath for producing a bright, lustrous electrodeposit of zinc containing zinc ions, and chloride ions and dissolved therein naphthol polyoxyalkylate having the formula:

where R is hydrogen or methyl, and x is about 8 to 20 and polyethylenimine having the formula:

where R is hydrogen, methyl, ethyl, propyl, hydroxyethyl, 2 hydroxy propyl, 3-hydroxy propyl, 2- aminoethyl, 2-aminopropyl, or 3-aminopropyl, and y is about 10 to about 20.

2. A bath composition as set forth in claim 1 wherein the polyethylenimine is dissolved therein at a concentration of about 0.5 to about 20 gms. per liter.

3. A bath composition as set forth in claim I wherein the naphthol polyoxyalkylate is dissolved therein at a concentration of about 0.5 to about 20 gms. per liter.

4. A bath composition as set forth in claim 1 wherein there is also present at least one of the substances selected from the group consisting of anisaldehyde, piperonal, veratraldehyde, benzaldehyde, vanillan, benzylidene acetone, and cinnamic aldehyde, and present in a concentration of about 0.01 to about 10 gms. per liter. 

2. A bath composition as set forth in claim 1 wherein the polyethylenimine is dissolved therein at a concentration of about 0.5 to about 20 gms. per liter.
 3. A bath composition as set forth in claim 1 wherein the naphthol polyoxyalkylate is dissolved therein at a concentration of about 0.5 to about 20 gms. per liter.
 4. A bath composition as set forth in claim 1 wherein there is also present at least one of the substances selected from the group consisting of anisaldehyde, piperonal, veratraldehyde, benzaldehyde, vanillan, benzylidene acetone, and cinnamic aldehyde, and present in a concentration of about 0.01 to about 10 gms. per liter. 